Drivers of Root Dynamics in Diverse Plant Communities

Periodic Reporting for period 1 - DiverseRoots (Drivers of Root Dynamics in Diverse Plant Communities)

Okres sprawozdawczy: 2016-01-01 do 2017-12-31

There is increasing evidence that interactions with the living soil are an important driving force behind the increased plant and root growth in mixtures to monocultures. Recent research shows that root growth of plant species in monocultures is restricted by their ‘own’ soil biota. Therefore, when plants are grown in multi-species mixtures this pathogenic effect is diluted by soil biota of other plant species.
The objective of this project is to apply state-of-the-art methodology to 1) assess to what extent biodiverse vegetation affects rooting structure and 2) elucidate the main drivers behind these rooting dynamics.
In a desk study, I analysed existing root data in order to assess the differences in horizontal root distribution in monocultures compared to mixtures. The results suggest a higher level of (interspecific) intermingling of plant roots in mixtures compared to monocultures, resulting in a more homogenous filling at the horizontal plane. As erosion resistance is determined by the weakest spot in the cover, these new results help in designing new plant communities for optimal erosion control, such as on river and sea dikes.
Additionally a root study was carried out in the unique Phytotron facility of Radboud University, to assess the effect of plant-soil feedback in soil patches (legacy effect) on the root biomass and root activity of species grown in species mixtures, using tracer techniques. Preliminary results show a significant difference in tracer concentration between the different species and soil legacy and evidence that the root activity of different species is differentially affected by the history of the soil its growing in.

WP1: Horizontal homogeneity of roots in monocultures and mixtures
I reanalysed the data from two unique datasets containing root data in which the root biomass and species identity of multiple root cores per experimental unit were measured separately in both monocultures and mixtures. The hypothesis was that if roots show more interspecific intermingling (which is expected as a strategy to avoid detrimental pathogens under the pathogen theory) as opposed to interspecific segregation (expected under the niche differentiation theory), this will result in less variation in horizontal root density in mixtures compared to monocultures.
For the whole plant community the observed horizontal variation in root density in mixtures tended to be lower than expected based on the variation in monocultures. Using a framework for estimating the variation at individual plant level, the variation in observed mixtures was generally lower than predicted based on monocultures, particularly for grasses. These results suggest a higher level of intermingling of plant roots in mixtures resulting in a more homogenous filling at the horizontal plane.
If indeed (specific) mixtures show a lower variation in horizontal root density compared to monocultures, this would be important information for the development of vegetation plans aimed at erosion control, such as on river and sea dikes.
A conference paper has been submitted to the Root Research International Symposium, Israel, 2018 and the scientific manuscript has been written and will be submitted soon.

WP2: Phytotron experiment
In species-rich plant communities, the distribution of soil biota is patchy as plant species develop their own communities of soil biota over time. There is increasing evidence that these communities are predominantly pathogenic. When plant individuals die, this results in a microbial legacy effect in the soil. The remaining microbial community may affect the belowground exploitation of these patches, i.e. root placement and root activity, and subsequent invasion by other species. The objective of this WP was to assess the effect of plant-soil feedback in soil patches on the root activity of species grown in mixtures. We hypothesise that root growth of species is more negatively affected in soil in which the species has grown before (“own soil”) than soil conditioned by other plant species (“foreign soil’) or mixed soil.
In 2016, a mesocosm experiment was set up in which we created 48 mixed plant communities containing eight different plant species consisting of four grass species and four forb species. Within each compartment we created four soil patches, containing soil preconditioned by one of four plant species or a mixture of all four soils. In June 2017, a tracer solution containing 15NO3, Rb, Li and Sr was injected into the patches in the mesocosms to assess nutrient uptake activity of the different species.
Preliminary analysis of the Rb, Li and Sr concentrations in the aboveground plant material indicated that there was evidence of interaction between patch type and plant species, indicating that the root activity of different species is differentially affected by the history of the soil its growing in, which may support our hypothesis. Further analysis is required to confirm how these preliminary tracer results compare to the 15N tracer results (in March 2018).
A conference paper has been submitted to the I Root Research International Symposium, Israel, 2018 and the scientific paper is to be completed in 2018.

WP3: Training and transfer of knowledge
This Marie Curie Fellowship has contributed greatly to my personal and career development:
At the RU, I have gained experience in a number of new research techniques in relation to root development and have participated in weekly internal seminars.
During my secondment at the Louis Bolk Institute, I have been involved in numerous aspects of research, networking and dissemination in subjects related to root development and grassland. I have participated and given presentations in numerous networking and stakeholder meetings and was involved in the writing of popular publications.

WP4: dissemination
In addition to the two scientific papers in preparation for WP1 and WP2, the work of WP1 and WP2 will be presented at the Root Research International Symposium 2018, Israel. Additionally, the work has been presented at a number of in-house seminars at the RU.

Career
This MC Fellowship has had significant impact on my career as a researcher. Through my interactions with Hans de Kroon and his group, I have deepened my knowledge on belowground plant interactions and have received training on root techniques. I have diversified my knowledge and skills in research and dissemination in root ecology in an agricultural setting during my secondment at the Louis Bolk Institute. I have started my new job as a researcherthe Louis Bolk Institute on the 1st of January 2018.

Science base
The results of WP1 are novel input in new research projects on the erosion resistance of dike vegetation projects. Dike vegetation is the first layer of protection against high water regimes, and the strength of the root mat determines its erosion resistance. WP1 gives new information how the variability in root cover depends on the composition of the plant community. As erosion resistance is determined by the weakest spot in the cover, these new results help in designing new plant communities for optimal protection. The Radboud University group of Hans de Kroon is in contact with water boards and engineers to bring these results into practice.
The results of WP2 are important for designing new research projects at Radboud University, but also for developing new applications at the Louis Bolk Institute.

Plant community in mesocosm experiment (WP2)

Filling of compartments for the mesocosm experiment (WP 2)

Periodic Reporting for period 1 - DiverseRoots (Drivers of Root Dynamics in Diverse Plant Communities)

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